Microwave dielectric ceramics (MWDCs) are pivotal to modern wireless communication systems, with their performance governed by three key parameters: relative dielectric constant (ε_r), Q×f value (product of quality factor Q (reciprocal dielectric loss) and frequency f), and temperature coefficient of resonant frequency (τ_f). This review systematically summarizes the recent research progress of MWDCs from five interrelated aspects. In terms of performance characterization, standardized resonant methods achieve ε_r measurement errors below 1% and a tanδ detection limit as low as 10^-5. Theoretically, frameworks from complex crystal chemistry to the recently elucidated cation rattling effect enable quantitative interpretation of dielectric behavior. In processing, the cold sintering process achieves ceramic densification below 300 °C, reducing energy consumption by over 97% in comparison with conventional sintering. For applications, these materials have been widely deployed in high-performance substrates, resonators, and filters for 5G/6G communications, with device insertion loss maintained below 1 dB. Additionally, data-driven approaches, particularly machine learning, can accurately predict key dielectric properties with a coefficient of determination (R²) higher than 0.9, accelerating the exploration and development of novel MWDCs. By integrating these perspectives, this review offers a systematic insight into the state-of-the-art progress and future development directions of MWDCs research.

For the regular preparation techniques of ceramics, high-temperature sintering has always been a necessary condition to obtain dense microstructures and good properties. As a recently emerged technique, Cold Sintering Process (CSP) can achieve rapid densification for various ceramic materials at ultra-low temperatures (below 350 ℃) through dissolution-precipitation and other mechanisms. CSP has shown tremendous development space and high research potential by effectively solving the problems existing in conventional high-temperature sintering in terms of energy consumption, microstructural control and co-firing with organics. This review starts from the brief summary on the development history, technologic process and densification mechanisms of CSP. Then the application status of CSP on the preparation of ceramics (including bio-ceramic materials, new energy materials, semiconductor materials, dielectric materials, thermoelectric materials, unstable materials at high temperatures) is described, and its future development is prospected.

BaTiO₃-epoxy dielectric composites were prepared by curing the liquid epoxy monomer that infiltrated into the partially-sintered BaTiO₃ porous ceramics. The BaTiO₃ volume fraction of the composites maintained around 58.6% with increasing the sintering temperature from 600 ℃ to 1000 ℃, while the significant microstructure evolution, improved connectivity of BaTiO₃ phase and dramatical increase in permittivity from 102 to 697 were observed. The permittivity and BaTiO₃ volume fraction further increased to 2328 and 83.5% for the sintering temperature of 1250 ℃. The present composites had the permittivity 1–2 orders of magnitude higher than the 0–3 type ones, and the extraordinary results were mainly attributed to the improved connectivity of BaTiO₃ phase that benefited from partial sintering. The connectivity also had a significant effect on the temperature dependence of permittivity, and good combination of temperature-stable high permittivity, low dielectric loss and relatively low ceramic fraction could be obtained by regulating the connectivity of BaTiO₃ ceramic phase.